You don't trade Smart to shuffle the deck. You cannot possibly have enough perimeter defenders, and the answer to "who's the fifth starter as Horford gets old" is just putting White in the starting lineup next to Smart and letting Rob/Al platoon the center position. If you somehow needed Smart to get a trade over the line that puts, like, Doncic next to the Jays (which isn't happening) then we can talk, but you don't move him for the sake of looking like you did something.
This summer isn't that hard, provided Jaylen makes an all-NBA team. Supermax Brown, make a pick in the 30s on draft night, package Pritchard and Gallo for a backup swingman, re-sign Grant, and otherwise use what contracts you can offer to add a veteran or two to the bench. That's all you have to do.
It only gets complicated if Jaylen can't be extended.